The present invention relates to a speaker used in a portable communication equipment such as a portable telephone and other equipments.
Referring to FIGS. 4 and 5 showing a conventional speaker, a yoke 2 made of magnetic material is embedded in a case 1 made of plastic by insert molding. A permanent magnet 3 is secured to the yoke 2, and a top plate 4 made of magnetic material is adhered to the magnet 3 to form a magnetic circuit and to form a magnetic gap between the top plate 4 and the yoke 2.
A vibrating plate 6 is secured to the case 1 at a shoulder 1b of the periphery thereof. A voice coil 5 secured to the underside of the vibrating plate 6 is inserted in the magnetic gap. A protector 7 made of metal is secured to the case 1, interposing the vibrating plate 6. A plurality of sound discharge holes are formed in the case 1 and the protector 7. The vibrating plate 6 and the protector 7 are positioned by a cylindrical peripheral projection 1a. 
A pair of ends 9 of the voice coil 5 are adhered to the underside of the vibrating plate 6 as shown in FIG. 4. Each of the ends 9 is outwardly extended from the case 1 passing through a groove 1c formed in a peripheral wall of the case. On the underside of the case 1, a substrate 8 made of plastic is adhered, and a pair of terminal plates 10 are secured to the substrate 8. Each of the terminal plate has a V-shape and each end 9 is connected to one of the branches of the terminal plate 10 by solder 11. The other branch of the terminal plate 10 is used for connecting the end 9 to a circuit of the equipment to be mounted therein.
Thus, when a signal current is applied to the voice coil 5 through the terminal plates 10, the vibrating plate 6 vibrates to produce sounds.
Another conventional speaker shown in FIG. 6 is different from the above described speaker in that a case comprises a lower case 22 and an upper case 23. The upper case 23 has a peripheral projection 23a and a shoulder 23b. 
The vibrating plate 6 is positioned by the peripheral projection 23a and the peripheral portion of the vibrating plate 6 is adhered to the shoulder 23b. The protector 7 is secured to the periphery of the vibrating plate 6.
The ends 9 of the voice coil 5 projected from a groove 23c formed in the upper case 23 are connected to the terminal plates of the substrate 8. The lower and upper cases 22 and 23 are adhered by an adhesive.
In the above described conventional speakers, the vibrating plate 6 is positioned by the peripheral projection 1a (23a) and secured to the shoulder 1b (23b). Therefore, the effective diameter of the vibrating plate 6 is reduced by double of width of the shoulder 1b. In order to improve the quality of the sound produced by the speaker, it is necessary to increase the diameter of the vibrating plate. However, the reducing of the diameter of the vibrating plate causes the quality of the produced sound to deteriorate.
An object of the present invention is to provide a speaker which may obviate the above described trouble.
According to the present invention, there is provided a speaker comprising a case having a peripheral projection, a yoke made of magnetic material and secured to the case, a permanent magnet provided in the case, a vibrating plate having a cylindrical periphery and secured to the case at the peripheral projection, a voice coil secured to an underside of the vibrating plate, and a protector plate secured to the case.
In an aspect of the present invention, the cylindrical periphery of the vibrating plate is adhered to the outside wall of the peripheral projection of the case.
In another aspect of the present invention, the cylindrical periphery of the vibrating plate is adhered to the inside wall of the peripheral projection of the case.
A peripheral portion of the vibrating plate is mounted on a top edge formed on an upper portion of the peripheral projection of the case.
The protector plate has a cylindrical periphery which is adhered to the outside wall of the cylindrical periphery of the vibrating plate.
These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.